Communication systems are known to transport large amounts of data between a plurality of end user devices. Such end user devices include telephones, facsimile machines, computers, television sets, cellular phones, personal digital assistants, et cetera. As is also known, such communication systems may be a local area network (LAN) and/or a wide area network (WAN). A local area network is generally understood to be a network that interconnects a plurality of end user devices distributed over a localized area (e.g., up to a radius of 10 kilometers) and includes LAN infrastructure equipment. For example, a local area network may be used to interconnect workstations distributed within an office of a single building or a group of buildings, to interconnect computer based equipment distributed around a factory or hospital, et cetera. As is further known, local area networks may be wired local area networks or wireless local area networks. Wired local area networks typically have a star topology, ring topology, bus topology or hub/tree topology.
A wide area network is generally understood to be a network that covers a wide geographic area and includes WAN infrastructure equipment. Wide area networks include both public data networks and enterprise wide private data networks. A public data network is established and operated by a national network administrator specifically for data transmission. Such public data networks facilitate the inner working of equipment from different manufacturers. Accordingly, standardizations by the ITU-T have been established for conveying data within public data networks. Currently, there are two main types of public data networks: packet switched public data networks and circuit switched public data networks. For example, the public switched telephone network is a circuit switched public data network while the Internet is a packet switched public data network. Other examples of wide area networks include integrated service digital networks (ISDN) and broadband multiservice networks.
As is further known, communication systems may be networked together to yield larger communication systems, where such networking is typically referred to as internetworking. Internetworking is achieved via internetworking units that allow communication networks using the same or different protocols to be linked together. The internetworking units may be routers, gateways, protocol converters, bridges, and/or switches.
Regardless of the type of communication system (e.g., LAN, WAN, or internetworking system), each communication system employs a data conveyance protocol to ensure that data is accurately conveyed within the system. In general, a protocol is a formal set of rules and conventions that govern how system devices (i.e., end user devices, LAN infrastructure equipment, WAN infrastructure equipment, and/or internetworking units) exchange data within the communication system. Such protocols typically include regulations on receiver sensitivity (i.e., how noisy a received signal may be and how small its amplitude may be) for signals received by a system device or within a system device and on transmit power of a signal from one system device to another or within the system device.
As is further known, each system device processes millions of bits of data per second. Accordingly, each system device includes high-speed data interfaces to efficiently input and output data. Such interfaces are typically implemented as integrated circuits that are mounted on a printed circuit board. A group of printed circuit boards may be mounted on a back plane and multiple back planes may further be placed in a rack to make up the system device.
In an effort to meet the ever-increasing challenges of improving data conveyance speed, each system device includes an increasing number of integrated circuits, printed circuit boards (PCBs), and/or racks. Typically, the racks and PCB's are coupled together using coaxial cables, fiber optics, connectors, and/or wires. The integrated circuits on a printed circuit board are operably coupled together via copper traces (e.g., FR4 connections). As the number and complexity of the system devices increases, along with the desired speed of conveying data therebetween, the distance between ICs, PCBs, and/or racks is increasing in diversity. Some communication channels between ICs, PCBs, and/or racks may be relatively short (i.e., have a channel response that introduces minimal distortion of the signals it carries) while others are relatively long (i.e., have a channel response that introduces significant distortion of the signals it carries).
Typically, a receiver section of a high-speed data interface includes an equalizer to compensate for the distortion produced as a result of the channel response. Typically, the equalizer is set to compensate for the channel response of a nominal channel. In other words, the equalizer is fixed to provide a nominal equalization response, which corresponds to the inverse of the nominal channel response. However, as the channel responses vary more and more due to the increasing diversity of channel lengths, a fixed equalizer is inadequate to meet the receiver sensitivity requirements of many standardized protocols.
Therefore, a need exists for programmable equalizer for use within receiver sections of high-speed data interfaces.